[BUG] New commits pushed to the base branch results in errors when shallow history is used.

[jackton1]

Is there an existing issue for this?

• I have searched the existing issues

Does this issue exist in the latest version?

• I'm using the latest release

Describe the bug?

See: #666

To Reproduce

1. Create 2 PRs from the base branch
2. Merge PR 1 into the base branch which changes the HEAD sha
3. Notice an error in PR 2 which has a reference to the fork point sha (This happens when fetch-depth is set to 1)

What OS are you seeing the problem on?

all

Expected behaviour?

A new input used to Limit the fetched history of the target branch.

Relevant log output

No response

Anything else?

No response

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